The prime objective of this project is to develop a broad understanding of the fundamental chemistry of metal ions utilized in radioimmunotherapy, of foremost interest being Pb(II) and Bi(III). To accomplish this objective, we need to learn the coordination chemistry of metal ions, in particular, their kinetic and thermodynamic behaviors in solution. This information can then be employed to develop radiolabeled antibody systems for use in therapeutic applications. Thus, 212Pb potentially serves as an in vivo generator for delivery of the alpha-particle emitter 212Bi. Additionally, the alpha-particle emitter 213Bi, also being developed as a therapeutic agent, has decay characteristics that obviate the requirement of a Hot Cell now used for 212Bi. Substantial progress continues in obtaining 213Bi from an 225Ac generator. Yields of up to 10 mCi were obtained for use in successfully radiolabel monoclonal antibodies. However, after a few days, radiolysis of the ion- exchange support resin resulted in failure of the generator. Studies initiated to solve this problem by employing a more stable ion-exchange support has resulted in development of a prototype silica based ion- exchange 225Ac/213Bi generator proposed to resist radiolytic failure. Preliminary tests with modest levels of 225Ac have demonstrated excellent chemical separations of the radionuclides without breakthrough or breakdown of the support. This developmental work continues to receive support in collaboration with the DOE and ITU and will progress pending increased supplies of the parent radionuclide.